(i) Field of the Invention
The present invention relates to a poly[(3-pyrrolyl)acetic acid] and a method for preparing it.
(ii) Description of the Related Art
It is already well known that a polypyrrole becomes electrically conducting upon oxidation. U.S. Pat. No. 3,574,072 also discloses that the polymerization of such a polymer can be electrochemically put into practice. Furthermore, the oxidation potential of the abovementioned polymer is extremely low (E.sub.ox =-0.1V/SCE), and the polymer in a doped condition also exhibits electroconductivity and is excellent in environmental stability. For these reasons, it is expected that this polymer can be applied to many fields, and therefore much attention is paid to the polymer.
With regard to the modification of physical properties of this polymer, it has been attempted to change dopants and to alter substituents of pyrrole. In connection with the substituents, the substitution on the nitrogen atom has been mainly studied. However, the N-substitution on the polypyrrole inconveniently results in a steep decrease in conductivity (&lt;10.sup.-3 S.multidot.cm.sup.-1) and a noticeable increase in the oxidation potential of the resulting polymer (E.sub.ox &gt;0.6V/SCE).
A recent work has reported the functionalization of the polymer by linking ferrocenyl groups to the 3-carbon atom of a pyrrole monomer through an alkyl spacer. It has been also reported that the 3- or 3,4-substitution of the pyrrole monomer has less influence on conductivity of the resultant polymer than the N-substitution.
With regard to a ferrocenylpyrrole monomer, the steric hindrance of a substituent does not allow the formation of a continuous homogeneous film. However, it is known that the above-mentioned problem has been overcome by copolymerizing substituted pyrrole with unsubstituted pyrrole so as to dilute the ferrocenyl group in the polymer.
On the other hand, it has been elucidated by various means that the electrochemical redox process of the polypyrrole include transports of the two electrolyte species, i.e., an anion and a cation in opposite directions inside the polymer These two ionic transports can be separated into two different redox systems by using a large-sized electrolyte anion, and the present inventors are under researches on the separation of an ionic process regarding a hydrophobic pyrrole.
In the wake of the above-mentioned researches, the present inventors have investigated the polymer of a pyrrole in which the 3-carbon atom is substituted with a carboxymethyl group, and as a result, they have found that the polymer can be obtained by conventional known electrolytic oxidation polymerization.